Composite material obtained from combining transition metal carbides and metal binders are widely used as raw material for cutting tools. Among the many subdivisions of such composite material, the main classes for cutting tools applications are tungsten carbide (WC—Co carbide) composites and titanium carbonitride (Ti(C,N) or TiCN) based cermets that have high toughness and good hardness.
Titanium carbonitride (Ti(C,N) or TiCN) is a solid solution of titanium nitride (TiN) and titanium carbide (TiC). As it comprises both constituents, titanium carbonitride enjoys both the high hardness of titanium carbide as well as excellent chemical stability and toughness of titanium nitride. Furthermore, it has superior resistance to oxidation and conductivity for heat and electricity and shows favorable resistance to creep and abrasion. Such qualities impart superior physical properties to cutting tools based on titanium carbonitride over those based on tungsten carbide.
Accordingly, titanium carbonitride powders find increasing use for cutting materials despite their high cost, the representative applications being cutting tools for manufacturing products and semi-finished products of steel and cast iron that require higher cutting speed than tungsten carbide tools.
Prior art methods for preparing titanium carbonitride powders were carried out in two stages in which powdered titanium carbide was first obtained followed by heating under a high pressure nitrogen atmosphere for extended periods at high temperatures to synthesize titanium carbonitride. Preparation of fine particles of titanium carbonitride in this way, however, was very difficult since the high temperature conditions caused abrupt growth of titanium carbide particles before their reaction with nitrogen.
On the other hand, mechanical properties required in cutting tools tend to improve as titanium carbonitride powder becomes finer and its purity higher. Accordingly, prior art methods relied on subjecting the synthesized titanium carbonitride powder to grinding, e.g., ball milling, to obtain fine particles less than a few micrometers wide. This was disadvantaged by long periods required for grinding due to the high hardness of titanium carbonitride.
For instance, a prior art reference on preparing a ultrafine TiCN matrix cermet (Zhang et al., Rare Metals, vol. 29 (2010), issue 5, p 528, Preparation and properties of ultra-fine TiCN matrix cermets by vacuum microwave sintering) teaches obtaining an ultrafine powder less than 1 μm wide by grinding commercially available powdered titanium carbonitride of an average particle size of 2.2 μm for 50 hours followed by microwave sintering under vacuum. The reference reports that such vacuum microwave sintering yields a TiCN cermet whose particles were finer, harder and denser than those obtainable from simple vacuum sintering.
At present, commercially available powdered titanium carbonitride has an average particle size of about 1-3 μm. There is a strong demand in the field for ultrafine grades of titanium carbonitride, i.e. grades finer than the currently available ones ranging from a few tens of to a few hundred nanometers. However, as mentioned above, the field still lacks a method for preparing ultrafine powdered titanium carbonitride that obviates the postsynthetic additional processing steps such as grinding and heat treatment. Accordingly, there is an unmet need in the field to develop an economical method for this purpose.